As is well known, almost all automobile bodies are monocoque bodies (unit construction bodies) in order to achieve both a lightweight and a high stiffness.
FIG. 20 is an explanatory view schematically showing an automobile body 1.
A monocoque automobile body is usually constructed by assembling a large number of components which are fabricated by press forming of a steel sheet having a thickness of at most 2.0 mm into a specified shape and connecting them by spot welding, for example. These many components for an automobile body (referred to below as automotive components) include, for example, a front side member 2, a bumper reinforcement 3, a front crash box 4, a front upper rail 5, a side sill 6, a floor cross member 7, a floor panel 8, a center pillar 9, a roof rail side member 10, a rear side member 11, and a rear crash box 12. In order to guarantee the required stiffness of the vehicle body, these components are constituted by one or more formed member body portions such as press-formed member body portions or roll-formed member body portions.
The term “formed member body portion” used herein means a body portion of a member in which the body portion has a ridge formed by a suitable bending technique such as press forming or roll forming of a sheet. In this description, it will be referred to for convenience as simply a formed member.
FIG. 21 shows an example of a formed member 13 which was fabricated by press forming of a flat sheet blank into a hat shape in cross section. Specifically, FIG. 21 is an explanatory view schematically showing the structure of a front side member, which is one example of an automobile component 15 which is constituted by assembling the formed member 13 and a flat closing plate 14.
As shown in FIG. 21, the formed member 13 has ridge portions 13c which connect one surface 13a with other surfaces 13b, as a result of which the stiffness of the automobile component 15 is increased.
Patent Document 1 discloses an invention in which a ridge portion of a formed member is a folded portion which is formed by folding a steel sheet. Patent Document 2 discloses an invention in which a built-up weld is provided on a ridge portion of a formed member. Patent Documents 3-5 disclose inventions in which quenching is carried out on a portion where a formed member requires strength to form a quench hardened portion.
In addition, Patent Documents 6 and 7 disclose inventions in which formed members are manufactured by inserting a brazing filler metal between two steel sheets, which are materials being worked, and performing brazing and shaping in a so-called hot pressing step.